The present invention relates to a multifunctional particulate additive for personal care and cosmetic formulations, and a process of making the same. More specifically, it relates to the following:
i) an additive composition that when added as a component in personal care and cosmetic formulations, can simultaneously serve one or more of the following purposes: i) improve the efficacy of sunscreen actives used as ultraviolet radiation (UVR) filters, ii) thicken hydrophilic solvents such as water, glycols, glycerine, and alcohols or mixtures of these solvents, iii) emulsify and stabilize oil droplets in oil-in-water (O/W) emulsions, and iv) function as an antioxidant;
ii) an additive that comprises a particulate-based thickener/gellant such as smectite clays and/or a particulate-based UV-filter such as titanium dioxide or zinc oxide, and certain types of dispersants or surface-modifiers for these particulate materials;
iii) natural polymer-based surface-modifiers that contain polarizable functional groups such as phenolic, catecholic, and other aromatic groups, as well as hydrogen bond-forming groups such as hydroxyl, phenol, carbonyl, and carboxyl groups, which in turn enable the adsorption of these macromolecules on a variety of particulate surfaces;
iv) natural polymer-based surface-modifiers of the type mentioned above, contained in the multifunctional additive, that can emulsify and stabilize oil droplets in an O/W emulsion, such that the polymer molecules act as an emulsifier/stabilizer when the multifunctional additive is used as a component in an O/W emulsion-based cosmetic formulation;
v) the use of the foregoing natural polymers as dispersants or surface-modifiers in order to increase the number-concentration of particles of the aforementioned particulate materials in a suspension, and/or to impart colloidal stability (stability against coagulation) of such suspended particles, which in turn promotes and/or preserves the thickening or UV-filtering ability of these particulate substances in cosmetic dispersions;
vi) an additive that can enhance the effectiveness of organic sunscreen-actives, and thus increase the sun protection factor (SPF), a measure of efficacy of UV-filters, of sunscreen products containing these UV-filters;
vii) the use of natural polymer-based surface-modifiers as components in the multifunctional additive, that are essentially polyphenols, by virtue of which the additive delivers antioxidant functionality;
viii) the use of surface-modifiers as components in the multifunctional additive, that are natural polymers, used in combination with natural thickeners, such as smectite clays, and natural particulate UV-filters, such as titanium dioxide and zinc oxide, catering to the consumer demand for the use of natural ingredients in cosmetics;
ix) a method of delivering various functional properties listed in section i), that are useful in personal care and cosmetic formulations, through a single additive and thus providing ease and cost-savings in product formulations;
x) an in-situ method for surface-modifying a particulate material such as smectite clays and thus producing the particulate in an aqueous gel, that allows the thickener functionality of the particulate to be realized in one or more hydrophilic solvents.
Examples of personal care and cosmetic products where the additive composition of the present invention may be used may include skin-care creams, lotions, facial creams, and sunscreens; hair care products such as shampoos, conditioners, colorants, and hair styling aids; liquid makeups, foundations, shaving creams and lotions. The additive can also be used in topical pharmaceutical formulations that can benefit from enhanced protection of the skin from harmful UV rays. The foregoing personal care, cosmetic, and pharmaceutical products can be in the form of oil-in-water emulsion or water-in-oil emulsion, or gel.
I. Particulate-Based Thickener
Smectite clays are a class of inorganic particulate materials that occur as stacks of individual, planar silicate layers referred to as platelets in the clay-literature.
Examples of smectite clays include montmorillonite, bentonite, bidelite, hectorite, saponite, and stevensite.
These clays are popular particulate gellants or thickeners for aqueous compositions, particularly oil-in-water (O/W) emulsions. Fundamentally, the formation of particulate gels is a manifestation of suspended colloidal particles forming a network structure that entraps and thus immobilizes the suspending medium. Clay-based gels may form when individual platelets or stacks of a few aggregated platelets (tactoids) engage in interparticle associations with their neighboring platelets. If these particle-to-particle links extend throughout the total available volume, a gel, comprised of a continuous, linked particulate structure that entraps within itself the suspending medium, is formed. Such interparticle associations are governed by the interplay between the attractive and repulsive forces that generally act between particles suspended in a liquid. Hydrodynamic effects due to the orientation of planar clay particles in a flow-field may also contribute to the rheological properties of clay suspensions.
Clearly, the strength of particulate gels will depend on the number of interparticle associations in a given volume of the gel, implying that the greater the number-concentration of suspended particles, the stronger is the gel. Also, a dominance of the attractive interactions over the repulsive interactions, the likelihood of which increases with decrease in interparticle separation distance, is required for suspended particles to associate with their neighbors. An increase in the number-concentration of particles will tend to reduce their separation distances, an effect that could be especially dramatic for planar particles since the separation distance between two adjacent platelets will vary along their lengths when their faces do not align in parallel configuration. Nonetheless, too strong an attraction between adjacent clay platelets may draw them into strong association or coagulation, minimizing the particle number-concentration, once such coagulation occurs via face-to-face associations. In fact, it is these attractive forces that hold the clay platelets together in a stack.
Considering the above, the key to making clay-based gels is to ensure that there is sufficient interplatelet repulsion for the clay platelets to exfoliate (delaminate or deflocculate) under shear, releasing a large number of platelets as individual platelets or tactoids having fewer stacked platelets, that would then be available to form a particle network. On the other hand, in order to form a voluminous network structure, the net interaction (the sum of attractive and repulsive forces) between the delaminated platelets must be such that they can remain xe2x80x9cboundxe2x80x9d (attracted) to their neighboring platelets without being drawn into coagulation with their neighbors via face-to-face association. Accordingly, the gel-network may form if the delaminated platelets, while being separated from the surrounding platelets by as thick as possible an intervening layer of the suspending medium, reside in a relatively deep minimum in free energy of interaction with the neighboring platelets. Albeit physically separated from their neighbors, the individual platelets are no longer free to move independently, being trapped in a free energy minimum, producing in effect a continuous particle network, and hence thickening or gelation. Yet another way by which clay-based gels may form is where clay platelets coagulate due to edge-to-face associations, forming the so-called xe2x80x9ccard-housexe2x80x9d structure described in clay literature.
Forming clay-based gels, as an outcome of the aforementioned phenomena, would require tuning of interplatelet forces, such as by modification of the clay-surface. Adding complexity, these attractive and repulsive forces may vary with the properties of the suspending medium. Evidence of this may be found in that the clay-based gels form far more easily in pure water than in hydrophilic organic solvents such as glycols, glycerols and alcohols.
It is therefore an object of the present invention to modify the surface of a particulate thickener/gellant, preferably a smectite clay, in a manner that provides for achieving the thickener-performance of the particulate material in water and/or in one or more hydrophillic solvents, particularly the solvents used in personal care and cosmetic product manufacturing. An underlying goal of such clay-surface modification is to stabilize the clay platelets against strong face-to-face aggregation, such that the suspended-state of the delaminated platelets may be preserved over extended time.
II. Particulate Sunscreens
Metal oxides such as titanium dioxide (TiO2) and zinc oxide (ZnO) can serve as ultraviolet radiation (UVR) filters since they can scatter as well as absorb UVR. Clearly, the greater the number-concentration of particles available to scatter and/or absorb UVR, the higher will be the level of UV protection conferred by these particulate sunscreens. Therefore, a highly deflocculated state is required for the suspended metal oxide particles to perform most effectively as particulate UVR-filters. The use of dispersants (surface-modifiers) that could provide the suspended metal oxide particles with sufficient interparticle repulsion for effective deaggregation or deflocculation, could ensure such a finely-divided state of the particulate UVR-filter materials, and therefore a high level of UV protection.
An object of the present invention, therefore, is to produce a particulate-based additive for water-based and/or hydrophilic organic solvent-based cosmetic formulations, which contain one or more particulate UVR-filter materials in the form of highly deflocculated particles. Such a state of dispersion is attained and preserved by using dispersants (surface-modifiers), particularly, non-gum, non-starch, natural polymers, in order to meet the consumer demand for the use of natural ingredients in cosmetic products. Since the aforementioned additive may also contain one or more water-swellable, layered silicates as thickeners, in addition to one or more particulate UVR-filters, yet another object is to include those natural polymers in the additive, that can serve as dispersants both for layered silicate and particulate UVR-filter materials.
However, a strong dispersing effect of a dispersant on clay platelets may tend to oppose thickening or gelation in smectite clay dispersions. Therefore, a critical object of the present invention is to identify and use those natural polymers as dispersants or surface-modifiers that can deflocculate particles of UVR-filters effectively, while facilitating exfoliation of clay platelets and stabilizing the same against face-to-face coagulation, without strongly impeding thickening or gelation by the clay platelets. Polyphenolic compounds are known for their ability to serve as antioxidants, the functional ingredients that are highly desirable in the manufacturing of many cosmetic and personal care products. In order to ensure that the particulate-based additive disclosed herein provides for antioxidant functionality, an essential object of the present invention is to use those natural polymers as dispersants for the particulate components of the additive, which are polyphenols.
III. Emulsifier
A vast majority of cosmetic products are emulsions, mostly oil-in-water emulsions, and some water-in-oil emulsions. Emulsifiers are used to make these emulsions in a stable form such that the suspended oil droplets remain stable against flocculation and coalescence (fusion or aggregation of two or more droplets to form a bigger oil droplet) over extended time. The prior art teaches that even finely divided solid particles of latex, shale, clay, and other solid particles can stabilize emulsified oil droplets by adsorbing at the oil-water interface. Thickeners are added to emulsions for stabilizing emulsion droplets against sedimentation, a process known as creaming for O/W emulsions.
An additional object of the present invention is to use one or more natural polymer-based surface-modifiers for the particulate components of the disclosed multifunctional additive, wherein the surface-modifier can also serve as an emulsifier in personal care and cosmetic compositions. Conceivably, once surface-modified by such a polymer, the particulate components of the additive, such as smectite clays and/or the metal oxide-based UVR filters, may be rendered in a form where they may actually contribute towards emulsion-stabilization by adsorbing as colloidal solids at the oil-water interface.
IV. Organic Sunscreens
Ultraviolet radiation-absorbing organics, such as octyl methoxycinamate, homosalate, octocrylene, octyl salicylate, oxybenzone, methybenzylidene camphor, phenylbenzimaidazole sulfonic acid, ethylhexyl triazone, methyl anthranilate, and avobenzone are oil-like substances that are generally emulsified into cosmetic compositions to deliver UVR protection functionality. European patent application EP 0 619 999 reveals that a synergy in SPF can be found when particulate inorganic oxides such as titanium dioxide, zinc oxide, and iron oxide are used in combination with an organic sunscreen. In EP 0 619 999, the average primary (single or completely deflocculated) particle size for the inorganic particulates is less than 0.2 micron. Also, according to a preferred embodiment, the oxide particulates are incorporated in cosmetic compositions containing an organic sunscreen, in the form of an aqueous dispersion prepared by milling the inorganic oxide in the presence of a dispersant such as a polyacrylate or derivatives thereof.
Nonetheless, during the course of the present invention, it was found that increased SPF of organic sunscreen formulations could not be achieved in every case, even though the formulations contained particulate materials including titanium dioxide (TiO2) at relatively high concentrations. Given, however, that the TiO2 material used was a pigment-grade material with an average primary particle size of 0.3 micron and a maximum particle size of 1 micron, rather than the particulate TiO2 prescribed in EP 0 619 999, with an average primary particle size of less than 0.2 micron. Obtaining particulate materials such as inorganic oxides and silicates with an average primary particle size of less than 0.1-0.2 micron will require expensive milling or separation techniques. It is, therefore, an object of the present invention to be able to produce a particulate-based additive for cosmetic and personal care products, which can enhance the SPF of organic sunscreens, even when the average primary particle size for the particulate components of the additive is larger than 0.2 micron. In such an additive, the particulate components, preferably, do not just include an inorganic oxide including the inorganic UVR-filters, but also a smectite clay such that the additive may provide for thickening or gelation of hydrophilic solvents used in the manufacturing of cosmetic and personal care products. Also, as indicated earlier, an essential object of the present invention is that the particulate components of the multifunctional additive disclosed herein would have to be surface-modified necessarily with a natural polymer, and to achieve the full advantage of the present invention, with a polyphenolic natural polymer, such that the additive may provide for antioxidant functionality. While some natural polymers (carboxymethyl cellulose and xanthan gum) are disclosed in EP 0 619 999, these natural polymers do not present any molecular or structural features or components (for example, phenolic groups) that would allow them to function as an antioxidant. Also, these polymers are generally not very effective as deflocculants or dispersing agents for particulate materials. These polymers, therefore, could not be considered suitable for producing the particulate-based additive conforming to the various objects of the present invention.
V. Surface-Modifiers
Polymers and surfactants are often used in modifying particle surfaces to achieve various properties, including the properties that provide for interparticle repulsion. It has been found that polymers, when adsorbed on particle surfaces, in an amount sufficient to cover more than 50% of the particle surface area, generally enable the particles to mutually repel one another due to what is called xe2x80x9csteric repulsionxe2x80x9d in colloid literature. If these polymers are ionic, their adsorption on surfaces imparts an electrical charge to the surfaces, which in turn leads to an electrostatic repulsion between the coated-surfaces, since the surfaces carry a like ionic charge.
Traditionally, clay platelets have been modified to produce what is known in the prior art as xe2x80x9corganoclaysxe2x80x9d by treating them with quaternary surfactants that can adsorb on the clay-surface via ion exchange (for example, as described in U.S. Pat. Nos. 5,075,033, 5,164,433, 5,358,562, 5,407,477, and 5,634,969). Modification of clays by adsorbing linear synthetic polymers has also been achieved in the prior art (e.g., see U.S. Pat. No. 5,721,306).
When using either a non-ionic polymer (e.g, polyvinyl alcohol) or a polyelectrolyte (ionic polymer) for modifying the surface of clay to be used as a thickener, the molecular weight, the molecular structure or shape, and the charge density of the polymer are important considerations. This is because the large spatial expansion of a high molecular weight, linear polymer (e.g., polyvinyl alcohol, polyacrylate, polystyrene sulfonate) may lead to a long-range steric repulsion that may oppose thickening. Additionally, a polyelectrolyte (e.g., polyacrylate) with a high charge density when adsorbed on the surface of dispersed particles may produce a strong electrostatic repulsion between the particles, which again may not be favorable for thickening. Also, a polyelectrolyte with a high charge density may be able to maintain flexible, coil-like conformation that supports strong, long-range steric repulsion, over a wide range of ionic strength, thus making it difficult for an added electrolyte to induce interparticle associations required for thickening. Furthermore, for example, an anionic polyelectrolyte with a relatively high charge density, may experience a strong repulsion from a particle that already has an anionic surface charge and, therefore, it may be impossible for such an anionic surface-modifier to adsorb onto a particle surface that carries a like charge. Additionally, a polyclectrolyte having a higher charge density, is likely to have a higher xe2x80x9chydrophilicityxe2x80x9d, and therefore a lower affinity for hydrophobic surfaces, such as the surface of an oil droplet in an emulsion.
Yet another object of the present invention, therefore, is to use particular macromolecules as dispersants for the particulate materials contained in the disclosed multifunctional additive for cosmetic compositions, that avoid the above-described complexities associated with the use of polymeric surface modifiers. A related object is to identify and use those macromolecular surface-modifiers that can provide for emulsifier/stabilizer functionality.
It would be beneficial to cosmetic formulators to have a multifunctional additive that not only serves as a thickener/gellant but also offers one or more additional features, such as enhancement of UV-protection, antioxidant functionality, humectancy, reduced skin irritation, and consumer perception-related values such as xe2x80x9cnatural additivexe2x80x9d. A further object of the present invention, therefore, is to select and use macromolecular reagents for the surface modification of particles contained in the additive of the present invention, which could provide one or more of the foregoing benefits.
VI. Natural Polymers as Surface-modifiers
Natural anionic polymers such as lignin, lignosulfonate, humate, and tannate adsorb on various particle surfaces, both hydrophilic and hydrophobic, and serve as dispersants or deflocculants or emulsifiers/stabilizers for these particles in suspensions or emulsions. These anionic polymers, essentially polyphenols, have a variety of functional groups including polarizable groups (that favor van-der-Waals interaction-driven adsorption) such as phenolic, catecholic, and other aromatic groups, as well as hydrogen bond-forming groups such as phenolic, hydroxyl, carboxylic, and carbonyl groups. Their molecular weight may vary from about 2,000 to about 200,000 or higher. Because of their functional groups and structural properties, these macromolecules can attach onto a variety of substrates via mechanisms such as hydrogen bonding, van der Waals, electrostatic, and hydrophobic interactions, as well as surface-complexation with multivalent cations such as calcium, aluminum, and magnesium. Being polyphenols, they are expected to serve as antioxidants.
Although lignin and lignosulfonate may be regarded as high molecular weight, anionic polymers, their conformations differ vastly from those of linear polymers in that they are highly cross-linked, network polymers having a molecular shape that is often described as being spherical. When adsorbed on a surface or an interface, they can stabilize suspended particles against coagulation via both electrostatic and steric repulsions. However, because of their near-spherical shape, the spatial range of steric repulsion that they provide is not as long as that found with a linear, high molecular weight polymer.
Humate polymers are known to undergo coil-to-globule transformations (an effect that reduces the spatial range of steric repulsion instilled by an adsorbed macromolecule) in the presence of electrolytes. The electrolyte concentrations where such transformations would occur may be expected to be lower for humates than for synthetic polyclectrolytes such as polyacrylates, or polystyrene sulfonates or polynapthalene sulfonates, having anionic charge densities that are inherently higher than that of humates. It should be noted that in humates, the anionic groups, such as phenolate and carboxylate groups, are sparsely distributed in their molecular structure, consisting primarily of aromatic rings, as opposed to in every monomeric repeat unit of a polymer. In accordance with one important embodiment of the present invention, therefore, a humate polymer promotes deflocculation (exfoliation) of smectite clays into their individual platelets and/or into thin stacks of platelets (tactoids) under an applied shear. Once a large number of suspended platelets and/or tactoids are made available, an electrolyte is added at a dosage where it brings about such association between the neighboring delaminated platelets, that produces thickening of the slurry, avoiding the strong face-to-face association between the platelets. Suitable electrolytes are, for example, sodium chloride and potassium chloride.
The use of lignins, lignosulfonates, humates, and tannates as dispersants, emulsifiers/stabilizers, and surface-modifiers has been disclosed in the prior art in connection with numerous industrial applications. These include drilling fluids, oil well cementing, dyes and paints involving organic and inorganic particulates, concrete, gypsum, ceramics and bricks, paper-sizing, wax, drilling fluid, and asphalt emulsions, binding and briquetting aids, and flotation reagents. In the studies that led to the present invention, natural polymers selected from the lignosulfouates, lignins, and humates were evaluated as dispersants for particulate gellants (e.g. smectite clays) and particulate UVR-filter materials to be used in cosmetic formulations. These polyphenolic natural, surface-modifiers, that can serve as antioxidants, have been found in the present invention to be instrumental in providing unexpected combination of properties to personal care and cosmetic compositions, including thickening, SPF enhancement, and emulsification/stabilization.
VII. Process for Making the Multifunctional Additive
In the prior art, surface-modified clays have been made using two processes that are basically as follows. In the first process, a surface-modifying reagent is added to an aqueous clay-slurry and the resulting mixture is agitated for a given period of time during which the reagent is allowed to xe2x80x9creactxe2x80x9d (e.g., ion-exchange) with the clay surface. After completion of the reaction, the slurry is filtered, and the filter cake dried and pulverized to produce the modified clay. In the second method, the clay is extruded along with the surface-modifying reagent, followed by drying and pulverizing of the extruded material. Clearly, in these processes, several costly unit operations, such as drying and pulverizing, are required. Also, in order to realize the functional properties (e.g., thickening) that require adequate delamination of the clay-platelets or good dispersion of any other co-existing particulate, the particulate-based products made by the foregoing processes would have to be incorporated into personal care or cosmetic formulations using high-shear mixing processes. An important feature of one embodiment of the manufacturing method of the present invention is, therefore, to produce a surface-modified particulate-based additive for personal care or cosmetic formulations in a manner and form that allow one or more of the aforementioned costly processing steps to be avoided, and provide for a great degree of simplicity and ease in incorporating the additive into personal care, cosmetic, and pharmaceutical formulations.
The present invention is directed to cosmetic, personal care, and topical pharmaceutical compositions, and additives therefor. More specifically, it is related to cosmetic, personal care, and topical pharmaceutical formulations that include an effective amount of a multifunctional additive composition, added as a component in these formulations, said additive improving the SPF (Sun Protection Factor) of these formulations containing inorganic and/or organic sunscreens, and providing at least one of the following additional functional benefits to the formulations:
i) thickening of hydrophilic solvents such as water, glycols, glycerine, alcohols, or mixtures of these solvents;
ii) emulsification/stabilization; and
iii) antioxidancy.
In accordance with a preferred embodiment of the present invention, cosmetic and personal care compositions, requiring one or more of the functional properties listed above, can be manufactured using the multifunctional-additive compositions of the present invention. Such an additive preferably contains one or more particulate-based thickeners, such as a smectite clay, colloidal silica, laponite, and/or alumina, and most preferably one or more smectite clays. According to one important embodiment of the present invention, the thickener particles are co-dispersed with particles of one or more particulate UVR-filters such as titanium dioxide, zinc oxide, or SUNSPERE (available from International Specialty Chemicals, ISP), and most preferably with the natural particulate sunscreens such as the metal oxides. Another important component of the multifunctional-additive compositions is a dispersant or surface-modifier for the foregoing particulate materials, selected from the family of polyphenolic, natural polymers such as lignosulfonates, lignins, humates, tannates, and derivatives thereof. In addition, these compositions optionally include one or more of the following components: electrolytes, defoamers, humectants, emollients for cosmetics, preservatives, whiteners, and the like.
A hydrogel is the most preferred form of the disclosed multifunctional-additive, where the particulate-based thickener and the UVR filter material(s) are dispersed in an aqueous medium that may contain one or more hydrophilic organic solvents such as glycols, glycerine, and/or alcohols. As for an essential component, the hydrogel also contains one or more dispersing or surface-modifying agent selected from the group of polyphenolic, natural polymers such as lignosulfonate, lignin, and humate, to ensure good dispersion and colloidal stability of the particulate material(s) contained in the hydrogel. The hydrogel form is preferred since the composition can be easily blended into a cosmetic formulation containing any additional functional ingredient (for example, an organic sunscreen), without requiring an excess of shear. Any high shear equipment, for example, a homogenizer, or colloid mill, or other types of batch or in-line high shear mixer can be used to produce the hydrogel. Alternatively, the compositions of the present invention may be produced in a powder form, wherein the particle-surfaces of the thickener and/or the UVR-filter material are pre-treated and surface-modified with the natural polymer, and then dried, e.g., to 10% by weight liquid, or less. As yet another way of producing the compositions of the present invention, the particulate-based thickener and/or the particulate UVR-filter, and the foregoing natural polymer-based dispersant, may be added individually as components of a cosmetic formulation intended to contain the particulate material(s) as being dispersed in a hydrophilic solvent.
According to a preferred method of making the multifunctional additives of the present invention, in the form of a slurry-based additive-concentrate (e.g., hydrogel), a mixture of a smectite clay and a particulate UVR-filter (TiO2 or ZnO) is added to an aqueous solution of the natural polymer (e.g., lignosulfonate), containing the dispersant at a dosage in the range of about 0.05-300% based on the total dry weight of the clay and the particulate UVR-filter, more preferably about 5-50% based on the dry weight of the particulate materials, and most preferably about 10-30% based on the dry weight of the particulate materials. The amount of clay and particulate UVR-filter material added is preferably in the range of about 1-65% by weight, based on the total weight of the slurry. The weight ratio of clay and TiO2 in the clay-TiO2 mixture is preferably in the range of 1:1 to 9:1, or in some cases, no TiO2 is used, or in other cases, no clay is added. The clay-TiO2 mixture is added incrementally while a solution of the natural polymer dispersant is kept under agitation. After the entire amount of particulate mixture has been added to the natural polymer solution, mixing is continued until the resulting slurry assumes a homogeneous texture i.e., free of clay lumps. The slurry is then fed to a high-shear/impact device, such as a pressure homogenizer, a colloid mill or other such devices. Upon passing through the high shear/impact device once, the slurry turns into a highly viscous, gel-like material that is referred to herein as a mastergel. Optionally, the slurry may be passed through the high shear/impact device for more than one time, preferably for two to three times.
The most preferred method of making the mastergel involves the following sequential steps: i) a particulate UVR-filter (TiO2 or ZnO) is added to an aqueous solution of the natural polymer (e.g., lignosulfonate); ii) the resulting slurry is homogenized in a high shear/impact device (e.g., rotor-stator mixer) for about 5-10 minutes; iii) smectite clay is added incrementally to the homogenized slurry of the UVR-filter while the slurry is kept under low-shear agitation using a paddle mixer or the like; and iv) the resulting mixture is fed to and passed through a high shear/impact device (e.g., pressure-homogenizer, colloid mill) for one to three times. The aqueous solution of the dispersant contains the dispersant at a dosage in the range of about 0.05-300% based on the total dry weight of the particulate materials, more preferably about 5-50% based on the dry weight of the particulate materials, and most preferably about 10-30% based on the dry weight of the particulate materials. The amount of clay and particulate UVR-filter material added is preferably in the range of about 1-65% by weight, based on the total weight of the slurry.
The mastergel can be subsequently diluted in a desired hydrophillic solvent using a mixer, before or during the preparation of a cosmetic product. It may be noted that in a preferred embodiment, a water-content of at least about 8%, preferably about 10% to about 30% by weight, based on the total weight of the natural polymer (e.g., lignosulfonate/lignin/humate) solution, is provided for one or more of these natural polymers to completely dissolve in solvents containing predominantly hydrophilic organic solvents such as glycols, glycerine, and/or alcohols.
It has been found that the dispersing effect of the natural polymer, e.g., lignosulfonate, could not be realized adequately when attempts were made to produce the mastergel in predominantly glycol-containing mixtures of glycol and water. For example, a clay-content of 20%, based on the total weight of the slurry, was required to make a mastergel having a Brookfield viscosity of 24,150 cps (@20 rpm) in 75:25 ethylene glycol-water mixture. This finding led the inventors herein to the aforementioned xe2x80x9caqueous mastergelxe2x80x9d approach for rendering clay as an effective thickener, even for hydrophilic organic solvents used in personal care and cosmetic compositions.
As used herein, the word xe2x80x9cparticulatexe2x80x9d refers to any organic or inorganic material so long as it is available as solid or liquid particles that do not dissolve in hydrophilic liquids, such as water, a hydrophilic organic liquid, and mixtures thereof, included as a component in the compositions of the present invention. Particulate further refers to any organic or inorganic material so long as it is contained in the foregoing compositions in the form of solid or liquid particles dispersed or emulsified in a hydrophilic liquid. Any particulate material that is either a thickener or a UVR-filter is useful in accordance with the present invention so long as it has a particle size distribution such that at least 90% of the particles have a size less than or equal to 30 microns. Preferably, at least 90% of the particles of the particulate adsorbent/absorbent material are colloidal in size ( less than 1 micron).
Although the natural polymer-based dispersants or surface-modifiers contained in the aqueous mastergel are non-gum and non-cellulosic natural polymers, the mastergel may contain one or more additional thickening agents besides swellable layered silicates, including gums and cellulosics, as well as proteins and polyacrylates. The amount of such a gellant may vary from about 0.1-5% of the weight of the mastergel. Additionally, the mastergel may also contain functional oils, dispersed as emulsion droplets, at a maximum amount of about 50% of the weight of the mastergel. Such oils, offering functional benefits to cosmetic products, include but are not limited to silicone oils, and vegetable or botanical or flower oils.
Any lignosulfonate, kraft lignin, sulfonated kraft lignin, oxylignin, sulfonated oxylignin, humate, sulfonated humate, tannate and/or sulfonated tannate as salts can be used as a natural polymer dispersant or surface-modifier. For the lignosulfonate and lignin, both hardwood and softwood lignosulfonate/lignin may be used. As used herein, xe2x80x9ckraft ligninxe2x80x9d and xe2x80x9clignosulfonatexe2x80x9d have their normal connotation, respectively, referring to the substance typically recovered from alkaline pulping liquor and the substance typically recovered from sulfite pulping process. On the other hand, humate refers to water-soluble salts of humic acid polymers. The most preferred dispersants include ultrafiltered or otherwise de-sugared lignosulfonate, oxylignin or oxylignin sulfonate, and humate as sodium salts. The preferred molecular weight of these dispersants is in the range 5,000-100,000. Examples of some preferred lignosulfonate and humate products for producing the additive disclosed herein include Ultrazine NAC, Vanisperse A, Maracell XC-2 (sodium lignosulfonates from Borregaard LignoTech, BLT), Borresol HA-2 (a potassium humate from BLT, but used in the sodium-form after base-exchanging), and Enersol SC (a sodium humate from American Colloid Company).
Derivatives of the foregoing natural polymers that are useful in making the multifunctional additive of the present invention include the following:
oxidized (for example, using air, ozone, and/or hydrogen peroxide) lignosulfonate or oxidized lignin;
co-polymers of lignosulfonate or of lignin with acrylate, acrylamide, styrene sulfonate, and napthalene sulfonate derivatives;
azolignosulfonate and azolignin;
formaldehyde condensate of lignosulfonate or of lignin or of humate or of tannate;
hydrophobically-modified lignosulfonate, lignin, humate, or tannate;
cationically-modified lignosulfonate, lignin, humate, or tannate;
amino lignosulfonates or amino lignins; and
alkylated and/or crosslinked lignosulfonate or alkylated and/or crosslinked lignin.
The hydrophilic solvent may be selected from the group consisting of any hydrophilic organic solvent, water, and mixtures. Preferred hydrophilic solvents have a hydroxyl or polyhydroxyl functionality, such as an alcohol, a glycol, polyglycol, glycerol, and the like. The alcohols can be monohydric alcohols or polyhydric alcohols that are linear or branched.
The ranges of proportions of the various key ingredients included in mastergel (or additive-concentrate) compositions are given in Table I, based on the total weight of the mastergel. It should be noted, however, that in accordance with one embodiment of the present invention, the additive-concentrate would invariably contain one or more particulate material. The preferred dosage range of mastergel compositions for incorporation into a cosmetic formulation is 0.5-100% by weight, based on the weight of the formulation. However, in accordance with an important embodiment of the present invention, cosmetic and personal care formulations can be manufactured by adding in the key ingredients listed in Table I, individually as components of the formulations. For such compositions of the present invention, the dosage of each of the ingredients will be at per with that calculated based on proportions of ingredients in mastergel compositions as shown in Table I and the aforementioned preferred mastergel dosage.
In order to illustrate the present invention clearly, the following data are presented. The following examples and data are included as illustrations of the invention and should not be construed as limiting the scope of the invention.